Van't Hoff Factor and Freezing pt depression

[Jay2910]

Question reads:

What is the freezing pt of saturated solution of LiF? Kb=-1.86 K/m

It came from the Kaplan Q bank.

The solution doesn't include the Van't Hoff Factor of 2 for LiF . . . . can someone please tell me why this is so? The answer( given the solubility of 3g/L) turns out to be -.186 Kelvin.

Any kind of clarity would be much appreciated!

Thanks in advance!

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[LoLCareerGoals]

HF is a weak acid. Don't think you can assume full dissociation of LiF into Li+, F-.
There was an earlier discussion how CaF2 was almost completely insoluble in water, this probably the same effect in play here.

 

[Jay2910]

Ohhh . .I didn't take that into account! Thanks much!